The present invention relates to the field of materials and specifically to a method for protecting an object from kinetic threats using armor including a glass-ceramic structure. The present invention also provides specific glass-ceramic materials, methods of making the glass-ceramic materials, items and methods of making the items all demonstrated as being useful in protecting objects from kinetic threats.
A sensitive object is often protected by armor interposed between the sensitive object and an approaching kinetic threat and as a result the kinetic threat impacts with the armor instead of with the sensitive object. The armor is configured to neutralize the kinetic threat by one or more methods such as deflection of the kinetic threat, destruction/deformation of the kinetic threat and dissipation of the kinetic energy of the kinetic threat. In the art, known mechanisms for dissipating the kinetic energy of the kinetic threat include deformation of the kinetic threat, deformation of the armor, absorption of the kinetic energy of the kinetic threat and distribution of the kinetic energy over a large area.
Sensitive objects in many fields are increasingly subject to increasingly dangerous kinetic threats.
In the past, kinetic threats in the field of sports were rare. The speed of sports such as motorcycling, automobile racing, skiing and bobsledding has increased to the point where the danger from kinetic threats resulting from collision with static objects has increased significantly. Since sport performance is adversely affected by increased weight, the use of massive armor and shielding devices is impossible, necessitating the use of lightweight but not necessarily effective protection devices. There is a need to provide lightweight but effective protection from kinetic threats for individuals involved in sports.
Modern automobiles are constructed from thin metal or plastic panels designed to minimize vehicular weight and thus increase performance and economy of fuel use. At the same time, the cruising velocity of automobiles has continuously increased. Both factors together have led to an increase in traffic casualties. Although the effects of sudden deceleration cause most traffic casualties, a significant percentage of traffic casualties result from the penetration of objects into the passenger volume of an automobile through the thin panels. In the field of personal transport, there is a need to provide lightweight protection from objects penetrating the passenger volume of personal transport vehicles such as automobiles.
Satellites and space exploration vehicles are generally not protected from kinetic threats due to the prohibitive unit weight cost of launching an object with sufficient armor into orbit and due to the fact that the risk of catastrophic failure, for example resulting from impact with a meteorite, has been judged to be very low. However, the increasing density of debris at desired orbit altitudes (“space junk”) increases the chance of such an impact occurring. In the field of aerospace, there is a need to protect satellites and other space vehicles from kinetic threats such as the impact of “space junk” with armor that weighs as little as possible so as to make launch financially feasible. Since satellites are generally not reparable, it is preferred that such protection be useful for protecting against multiple kinetic threats.
In the past, non-military vehicles and installations were not targets for attacks from kinetic threats. Fragment-projecting explosive devices, high-velocity firearms, especially automatic firearms, and large caliber firearms have become increasingly available and at the same time, the will to use these devices and firearms by both criminal and terrorist organizations against civilian and other non-military targets has increased. As a result traditionally “soft” vehicles such as civilian buses and trains, limousines, fuel transport vehicles, police vehicles, logistical vehicles such as trucks and light utility vehicles are increasingly hardened. Traditional armors are heavy. The increase in weight caused by the addition of sufficient armor reduces vehicle mobility, maneuverability and stability, requires a massive and expensive frame, and leads to greater wear and consequent increased acquisition and operating costs. In the field of civil defense and crime fighting there is a need for lightweight, simple to produce and cheap armor to neutralize kinetic threats to military, non-military and civilian vehicles.
Metal armor is generally chosen for protecting combat vehicles and military aircraft from kinetic threats. Increasingly, requirements for air transport and amphibious operation requires that lighter weight armor solutions be found. Prior-art ceramic armors are effective against single kinetic threat impacts but are significantly less effective against the increasingly common multiple and serial kinetic threats posed by fragment-projecting devices, cluster weapons and automatic weapons. There is a need for high-performance, lightweight materials for use in military armor applications with multiple-threat neutralization capabilities.
Individual armor became outmoded with the introduction of firearms. For the first half of the twentieth century it was believed that the small size and mobility of an individual person conferred sufficient defense from kinetic threats and was preferable to weighing down the individual with massive armor. With the increased availability and use of fragment-projecting explosive devices and high-velocity automatic firearms, the survivability of an individual subjected to standard kinetic threats is significantly reduced. As a result individual body armor is becoming standard equipment for high-risk individuals, police and infantry soldiers. However, current body armor materials are either too bulky, reducing the efficacy of the individual in performing standard tasks when worn, or provide insufficient protection from increasingly effective kinetic threats. Further, both fragment-projecting devices and automatic weapons produce multiple kinetic threats for which the protection afforded by currently available body armor is insufficient. In the field of personal defense, there is a need for lightweight body armor protection capable of protecting an individual from multiple kinetic threats such as produced by fragment-projecting explosive devices and high-velocity automatic firearms.
Materials used in currently available armors can be divided into three types: textiles, metals and ceramics.
Textile armors are considered lightweight, easy to produce, simple to install and relatively comfortable to wear as body armor. When a kinetic threat impacts textile armor, the kinetic threat is caught in a web of fibers. The fibers absorb and disperse the energy of the impact to other fibers. Specific textile armors include textiles woven from aramid fibers, e.g. Kevlar® (E.I. du Pont de Nemours and Company) and Twaron® (Teijin Twaron B.V., Arnhem, The Netherlands) and textiles based on polyethylene fibers, e.g. Dyneema® (Koninklijke DSM N.V., Heerlen, The Netherlands). Generally, textile armors are suitable for protecting against low energy threats such as shrapnel small caliber bullets having impact velocities up to about 450 m sec−1 but are useless against specially designed armor-piercing rounds and bullets from high-velocity firearms having typical impact velocities of 900 m sec−1 unless used in conjunction with a metal or ceramic strike face.
Metal armor provide excellent protection from kinetic threats, are cheap and relatively easy to produce from alloys, usually including aluminum, cobalt, titanium and iron. A kinetic threat impacting metal armor is deflected or deformed and the kinetic energy dissipated by inelastic and elastic deformation of the armor. Metal armor is effective against multiple kinetic threats since damage to the armor caused by the kinetic threat is generally local to the area of impact. However, the weight of metal armor is such that providing sufficient protection against increasingly common kinetic threats is often impractical.
Although expensive, armor made of ceramic plates provides a high level of protection from kinetic threats and is light in weight in comparison to equivalent metal armor. Ceramics most often used for protection of objects from kinetic threats are monolithic ceramics such as Al2O3, B4C, SiC and AlN.
A kinetic threat impacting ceramic armor is deformed and the kinetic energy dissipated by inelastic deformation of the armor through a combination of a pulverization energy mechanism and a fracture energy mechanism. In the pulverization energy mechanism, a comminution zone of pulverized ceramic in the shape of a conoid emerging from the impact point is produced. In the fracture energy mechanism, kinetic energy is absorbed by the ceramic plate, distributed throughout the plate and subsequently expended by the shattering of the ceramic plate itself along many radial and circumferential cracks. A liner, usually of textile or metal armor located behind the ceramic, absorbs and dissipates any residual kinetic energy of fragments of the ceramic armor and of the kinetic threat. The use of ceramic materials for protecting objects from kinetic threats is discussed in, for example, Medvedovski, American Ceramic Society Bulletin (2002), 81 (3), 27-32 and U.S. Pat. No. 3,765,600, U.S. Pat. No. 4,953,442, U.S. Pat. No. 4,911,061, U.S. Pat. No. 4,138,456, U.S. Pat. No. 5,456,156, U.S. Pat. No. 5,469,773, U.S. Pat. No. 5,705,764, U.S. Pat. No. 6,112,635 and U.S. Pat. No. 6,408,733.
In the art it is known that energy dissipation through the fracture energy mechanism is most efficient in ceramic materials that are hard, stiff and have a high sonic velocity. A high stiffness leads to maximal post-impact stress in the ceramic with very little elastic deformation whereas a high sonic velocity spreads the stress throughout the ceramic plate before actual shattering occurs. Ultimately, the impact energy of the kinetic threat is dissipated by the cleavage of many chemical bonds of the ceramic plate, thereby shattering the entire ceramic plate, see for example U.S. Pat. No. 5,469,773. Very hard ceramics are preferred so as to deform the kinetic threat in order to dissipate some kinetic energy and to reduce the chance of follow-through penetration subsequent to ceramic plate shattering.
Due to improved mechanical properties, ceramic-matrix composites are increasingly used instead of monolithic ceramics for protecting objects from kinetic threats. The primary advantage of ceramic-matrix composites compared to monolithic ceramics is improved mechanical properties. Suitable ceramic-matrix composites include fiber-reinforced materials such as Al2O3/SiC and Al2O3/C, ceramic/particulates such as TiB2/B4C and TiB2/SiC and cermets such as SiC/Al, TiC/N and B4C/Al. Ceramic-matrix composites are generally prohibitively expensive to manufacture and process.
The fact that the kinetic energy of an impacting kinetic threat is dissipated by shattering of the ceramic plate means that ceramic armor is generally useful for protecting an object only against impact from a single kinetic threat. Due to the extensive shatter of the ceramic, subsequent impacts have a statistically significant chance to impact on a crack and penetrate with little or no resistance. Further, the shards of the ceramic armor produced by the shattering are relatively small and have little mass: the small size means that there only a few bonds are available for dissipation of energy from subsequent kinetic threat impacting on such a shard and that such a shard may be pushed through by an impacting kinetic threat into the sensitive object being protected.
One method to provide multiple kinetic threat protection involves using many small ceramic scales to cover the surface of a protected object. When an individual small ceramic scale shatters, the protected object is still substantially protected from subsequent threats. Such solutions have many disadvantages, including the high price, added manufacturing complexity and the existence of chinks between any two ceramic scales. Multiple kinetic threats such as those projected by automatic weapons or cluster weapons can incidentally impact at the chinks in the armor or areas where ceramic scales were destroyed by previously impacting kinetic threats. As with shards, the small size of each individual scale means that the amount of energy potentially dissipated is relatively small.
A class of material not often used for protecting against kinetic threats is the family of glass-ceramics.
In U.S. Pat. No. 4,476,653 is taught the use of a glass-ceramic material as armor. A composition of U.S. Pat. No. 4,476,653 includes Li2O (9.5%-15% by weight), Al2O3 (1.0%-6.0% by weight), SiO2 (78.5%-84.5% by weight) and K2O (1.0%-4.0% by weight) as lithium disilicate, cristobalite and spinel crystals in a glassy matrix, where the essential nucleation agent is a combination of TiO2, ZrO2 and SnO2 in a ratio of 3:2:1. A preferred glass-ceramic of U.S. Pat. No. 4,473,653 is reported to have a hardness of between 4.95 and 6.23 GPa, a density of 2.4-2.5 g cm−3 and a coefficient of thermal expansion (TCLE) of greater than 100×10−7° C.−1. The maximal TiO2 content in a composition of U.S. Pat. No. 4,473,653 is 3%. The impact of a single kinetic threat (7.62 mm copper jacketed bullet at 152 cm with a muzzle velocity of 777 m sec−1) on a 21.7 mm thick glass-ceramic plate of U.S. Pat. No. 4,476,653 leads to shattering of the plate.
In U.S. Pat. No. 5,060,553 is taught the use of monolithic, sintered or hot-pressed glass-ceramic plates for use as armor. Suitable glass-ceramics according to the teachings of U.S. Pat. No. 5,060,553 are silicates of lithium zinc, lithium aluminum, lithium zinc aluminum, lithium magnesium, lithium magnesium aluminum, magnesium aluminum, calcium magnesium aluminum, magnesium zinc, calcium magnesium zinc, zinc aluminum, barium silicate and both calcium phosphates and calcium silico phosphates. In a first embodiment of the teachings of U.S. Pat. No. 5,060,553 is disclosed a composition that includes, in addition to other components, 7% by weight Al2O3 and 72% by weight SiO2 having a density of 2.45 g cm−3, a hardness of 5.7 GPa, and an elastic modulus of 104 GPa. In a second embodiment of the teachings of U.S. Pat. No. 5,060,553 is disclosed a composition that includes, in addition to other components, 13% by weight Al2O3 and 71% by weight SiO2 having a density of 2.4 g cm−3, a hardness of 5.25 GPa, and an elastic modulus of 88 GPa. In a third embodiment of the teachings of U.S. Pat. No. 5,060,553 is disclosed a composition that includes, in addition to other components, 33% by weight Al2O3 and 36% by weight SiO2 having a density of 3.1 g cm−3, a hardness of 10.8 GPa, and an elastic modulus of 150 GPa. In a fourth embodiment of the teachings of U.S. Pat. No. 5,060,553 is disclosed a composition that includes, in addition to other components, 26% by weight Al2O3 and 50% by weight SiO2 having a density of 2.7 g cm−3, a hardness of 6.0 GPa and an elastic modulus of 105 GPa. Although a mechanism for energy dissipation of an impacting kinetic threat is discussed, no report as to the actual ability of the compositions in neutralizing kinetic threats is presented.
In U.S. Pat. No. 5,045,371 is taught armor including ceramic particles dispersed in a glass matrix. In U.S. Pat. No. 5,469,773 is taught armor made of a composition including 92% MgO ceramic powder hot pressed with glass. These materials are not glass-ceramics.
It would be advantageous to have a material that provides protection from a kinetic threat on par with that of ceramics known in the art yet is lighter, is cheaper to manufacture and is more effective against multiple kinetic threats.